Twitter, Facebook and Apple have all announced that they were attacked by sophisticated cybercriminals. The New York Times revealed its experience with hackers in a front-page article last month. The Wall Street Journal and The Washington Post have also said they were attacked by what they believed to be Chinese hackers.

The revelations come as computer security experts estimate that more than a thousand companies have been attacked recently. In 2011, security researchers at McAfee unearthed a vast massive online espionage campaign, Operation Shady Rat, that found that more than 70 organizations had been hit over a five-year period, many in the United States.

Yet few admit to it. A majority of companies that have at one time or another been the subject of news reports of online attacks refuse to confirm them. The list includes the International Olympic Committee, Exxon Mobil, Baker Hughes, Royal Dutch Shell, BP, ConocoPhillips, Chesapeake Energy, the British energy giant BG Group, the steel maker ArcelorMittal and Coca-Cola.

What makes some companies admit to a hacking incident? Some step forward in the interest of increasing awareness and improving security within their respective industries. But often their candor is to little avail anyway.